Reserve power units (RPUs) are used to provide backup power in the event of power loss and are typically implemented using generators and/or electrical energy storage devices. The energy storage devices generally include batteries or capacitors, and are often used to provide power to perform safety functions or operations within a process control system, such as moving a valve or other process control component to a safe shutdown position (e.g., a failsafe position). Many energy storage devices are either rechargeable and/or easily replaceable.
The function(s) or operation(s) performed using the power from the energy storage device may not require all the energy in the energy storage device. In some applications, the presence of remaining energy in the energy storage device of an RPU is problematic. Many RPUs currently in use do not control or fully discharge remaining energy in the energy storage device and, thus, are not suitable for use in certain applications or environments.